Quantitative photovoltaic evaluation of the resistivity homogeneity of germanium single crystals

Abstract An apparatus, based on the bulk photovoltaic effect, is described by means of which quantitative estimates of the resistivity changes throughout germanium single-crystal samples may be realized. The experimental technique consists of scanning the sample with a light spot and recording the photovoltage, or integrated photovoltage, versus position of the light spot. By taking into account the magnitudes of the photovoltages and photoconductance upon illumination, the resistivity changes in Ω-cm can be derived from the scans of integrated-photovoltage versus position. For germanium of 10 Ω-cm resistivity or less, the changes in resistivity determined by the use of this system are usually within 30 per cent of the actual changes determined with the two-point probe. For material that is homogeneous in lifetime, the error may be as little as 3 per cent. With this technique, single-crystal wafers may also be explored so as to determine sections of best uniformity. The method is essentially non-destructive.